As described in U.S. Pat. No. 4,592,700 to Toguchi, vortex pumps are employed for pumping liquids that contain a substantial amount of foreign matter such as solids and/or fibriform matter. Because the foreign matter is a clogging hazard, the art has developed to provide a vortex chamber through which the pumped material generally passes, with an adjoining recessed chamber in which the impeller is rotatingly mounted. In some of these applications, at least the upper portion of the blades of the impeller extends into the vortex chamber, but the clear preference in avoiding contact between the foreign matter and the impeller is to have the entire impeller contained within the impeller chamber. The inventive concept disclosed in Toguchi '700, for example, involves an impeller in which the height of the blades is varied, so that some blades extend axially into the vortex chamber, while other blades do not.
As is also known from other prior art, including U.S. Pat. No. 4,676,718 to Sarvanne and U.S. Pat. No. 5,486,092 to Borg, the trade-off presented by avoiding contact of foreign matter with the impeller is a loss of efficiency and head when compared to a more conventional centrifugal pump.
It is therefore an unmet advantage of the prior art to provide unexpectedly improved efficiency and head from that of a vortex pump impeller as previously known.